1. Field of the Invention
This invention concerns a chamber for chromatographic analysis, in which temperature conditions as necessary for the analytical use of packed or capillary chromatographic columns are obtained. The chamber is particularly suitable for use with thin-walled columns, such as fused silica columns. The chamber comprises in a known way, a thermally insulated space which can be sealed towards the outside, and housed within the space are means for air heating and at least a fan for air circulation inside the closed space.
2. DESCRIPTION OF THE PRIOR ART
Chambers of the above defined type are already known and used, in particular chambers in which the fan is of the type with axial or axial-radial suction and with radial delivery, and it is mounted near an inner wall of the chamber, behind a screen having a central opening to allow air to reach the fan, as well as with its edge spaced from the other internal walls of the chamber to create passage for the air flow, beyond the screen, towards the column. The heating means, generally consisting of electrical resistors, are positioned, in said known chambers, coaxially to the fan, with a suitable distribution, in general a uniform distribution, on the outside of the fan itself. In this way, a circulation inside the airtight space defined by the chamber is created, starting from the section area of the fan, in correspondence with the central opening of the screen, passing through the fan, where the fluid flow threads or lines are accelerated to be sent in contact with the electrical resistors, and finally reaching the the space occupied by the chromatographic column(s) beyond the edges of the screen.
This known solution has shown problems especially when using thin-wall capillary columns, such as fused silica columns, which have the inconvenience of an extremely reduced thermal inertia and therefore, a very high sensitivity to temperature changes, namely to quick local and time variations versus nominal values. In fact, it has been noticed that the analytical results sometimes are not correct (distorted or divided peaks) due to the fact that the temperature at any point of the column undergoes rapid changes in time versus its nominal temperature. This is due to an imperfect mixing of the flow threads or lines of cold and hot air, which contact the column in a casual way. The temperature variation at different points of the column produces, in the case of thin-walled capillary columns, an almost instant variation in the distribution of the components within the mobile and the stationary phase, in the mentioned points. As a result, a distortion of the peak occurs and such distortion, especially in the end section of the column, can no longer be eliminated or attenuated by the remaining stationary phase. The peak remains distorted or even divided until it enters the detector.